It’s C. hope this helped and good luck !!
Answer:

Step-by-step explanation:

Use pythagorean theorem for all of them
a. 3, 4, 5
3^2+4^2?5^2
9+16?25
25=25
right
b. 5, 6, 7
5^2+6^2=7^2
25+36=49
61>49
acute
c. 64+81=144
145>144
acute
hope this helps!
You can use ruler and stuff and yea